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Polymarket US has begun quietly testing multi-leg sports contracts, opening a new front against Kalshi in one of prediction markets’ most lucrative product categories.
Since its first parlay-style trade on Aug. 5, Polymarket US has processed roughly $7.4 million across 16,173 trades, according to Gambity’s analysis of exchange data. The product remains in beta and has not received a broad rollout across Polymarket US’ consumer platforms.
Kalshi is operating at a much larger scale. The same analysis estimates that Kalshi collected approximately $25 million in taker fees from combo markets during the first 16 days of August alone. Kalshi calls its multi-leg products “combos” rather than parlays. The $25-million figure is an estimate based on trading data and fee schedules, rather than company-reported revenue.
Polymarket US laid the regulatory groundwork in May.
On May 20, QCX, which operates as Polymarket US, self-certified its Combinatoric Athletic Outcome Contract with the Commodity Futures Trading Commission (CFTC). The filing describes a contract combining two or more underlying sports contracts, where every selected leg must satisfy its payout condition for the combined contract to settle at $1.
Each contract has a $1 notional value, requires 100% margin of the amount at risk, and carries a $25,000 position accountability level. The filing does not impose a formal position limit. Polymarket US also prohibits certain athletes, coaches, employees, and other people connected to the underlying event from trading relevant contracts.
The structure puts Polymarket US closer to sportsbook-style products while keeping the transaction inside a CFTC-regulated event-contract exchange.
Its existing sports catalog already covers winners, spreads, totals, futures, and qualification markets.
Kalshi’s advantage is not simply that it launched first; it has already built infrastructure specifically around combo liquidity.
Its combo builder lets traders create custom combinations across sports and other eligible events. Pricing uses a request-for-quote system, where liquidity providers respond to a trader’s requested combination. Longer or less liquid combinations may receive no quote at all.
Kalshi has also paid directly to deepen those markets. Its Combo Incentive Program allocated $1 million for June 6 through June 30, plus another $200,000 for cryptocurrency-related events, with rewards distributed to qualifying liquidity providers.
That liquidity is feeding an increasingly valuable fee business. Kalshi’s standard fee formula charges takers based on contract quantity and probability, while maker fees, where applicable, are substantially lower.
The economics can also be punishing for traders. A recent analysis of Kalshi combo activity found buyers staked $226 million over a 14-day sample in July and lost $79 million, equivalent to $0.35 for every dollar staked.
The fight is happening in a much larger market than even a year ago.
Kalshi, Polymarket, and Polymarket US generated a combined $50.59 billion in July trading volume, up 7.8% from $46.95 billion in June. Polymarket US volume alone increased 54% month-on-month, while the international Polymarket platform declined 26%.
Polymarket US, therefore, enters parlays with growing underlying activity, but its $7.4 million beta remains small next to Kalshi’s established combo business.
The next test comes when Polymarket opens the product more widely. At that point, the contest will be less about who can list multi-leg contracts and more about who can consistently quote them, fill them, and turn that flow into fees.
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